2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177208We present here a timing analysis of the fastest accreting millisecond pulsar IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We corrected the arrival times of all the events for the orbital (Doppler) effects and performed a timing analysis of the resulting phase delays. In this way we find a clear parabolic trend of the pulse phase delays showing that the pulsar is spinning up as a consequence of accretion torques during the X-ray outburst. The accretion torque gives us for the first time an independent estimate of the mass accretion rate onto the neutron star, which can be compared with the observed X-ray luminosity. We also report a revised value of the spin period of the pulsar.Proceedings of the Frascati Workshop 2005: Multifrequency Behaviour of High Energy Cosmic Sources, Vulcano, May 23-28. 7 pages including 1 figureAstrophysicstext